Until now, researches about synthesis of the multi-substituted naphthalene lactone backbone of arylnaphthalene lignan-based natural products have been carried out in 4 ways as described below.

In the synthesis methods based on tandem Horner-Emmons-Claisen condensation and Diels-Alder addition, an Ar group is introduced in the initial stage of synthesis and, after a naphthalene backbone is formed under strongly basic or acidic conditions, a lactone structure is formed in the final stage using a reducing agent. Accordingly, use of Ar groups that are reactive under strongly basic or acidic conditions and in the presence of a reducing agent is limited. Also, in the synthesis methods based on palladium-catalyzed [2+2+2] cycloaddition and gold-catalyzed intramolecular sequential electrophilic addition and benzannulation, since an Ar group is introduced in the initial stage of synthesis, the methods are limited to Ar groups which are not reactive in the presence of the palladium or gold catalyst. Besides, it is impossible to selectively obtain the desired products since the position of the carbonyl group of lactone cannot be controlled.
That is to say, all the methods known thus far, including the above representative synthesis methods, involve addition of Ar groups having aldehyde, alkyne or aryl halide groups in the early stage of synthesis. Accordingly, these methods are not effective for synthesis of arylnaphthalene lignan derivatives and are applicable only to limited types of arylnaphthalene lignan compounds that can endure the reaction conditions of several steps until the final compounds are obtained.
The inventors of the present disclosure have invented a method allowing preparation of various kinds of arylnaphthalene lignan compounds without such limitations.